Field-pole for dynamo-electric machines.



H. POTH.

FIELD POLE FOR DYNAMO ELECTRIC MAGHINES.

APPLICATION FILED MAR. 9, 1906.

91 9 ,458, Patented Apr. 27, 1909.

3 SHEETS-SHEET 1.

H. POTH. FIELD POLE FOR DYNAMO ELEGTRIG MACHINES.

APPLICATION FILED MAR. 9, 1906.

. 2. w. m m m L 1 B m m M w mm A H 641 m d 3 Aw I m. 4 4 4 I L /a .m W a P 0v 2 w w WW l I I I l I I Il v H Q @44 52 I a %w f MW i a; V w y o 0 Q 8 M 5 m. 9 1 9 0 H. POTH.

FIELD POLE FOR DYNAMO ELEGTRIG MACHINES.

APPLICATION FILED MAR. 9, 1906,

I Patented Apr. 27, 1909.

3 SHEETS-SHEET 3.

HEINRICH POTH, or BROOKLYN, NEW YORK. I FIELD-POLE FOR numb-ELECTRIC aims.

I no. 919,458.

Specification OfLQttei'l l 'atent Patented-April 2 7,

Application filed larch 9, 1908. 8311180358391.

To all whom it may concern:

' Be-it known that I, Hnnmron Porn, a subject of the German Emperor, and a resident of Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Field-Poles for Dynamo-Electric Machines, of which the following is a specification. I My invention relates to the construction of pole pieces for decreasing or'entirely doing away with the cross magnetizing effect of the armature, and is designed as an improvement upon field poles having recessed pole pieces for this purpose. I l' The load limitations of a dynamo electric machine are fixed either by excessive spark formation or by the heating. If a direct current dynamo or motor is to run at all loads between no load and full load without sparking' and without shifting the brushes, then there must be only a small distortion of the a magnetic field, the cause of which is the cross-magnetizing effect of the armature current. The smaller this distortion or the smaller also the weakening of the commutating field, the easier will it be to obtain the ponditions of sparkless operation for high oads.

The heretofore known and used means for preventing or-decreasing thecross-magnetizing consist either in highly saturating the armature teeth and the pole horns or in attempting to increase the resistance to the" passage of the cross magnetizing lines of force by inserting air gaps. Under high loads, however, a satisfactory operation cannot be obtained by this means alone.

The object of the present invention is a pole construction in which the cross-magnetizing is reduced to thesmallest amount in one or several parts of the pole in accordance with circumstances and a greatest possible stability of the ordinary field as well as a considerable sa'ving-i'ncopper is thereby obtained.

' Figure 1 is a diagram showing the construction of the pole with a central air space bridged by magnetic paths. Fig. 2 is a similar View showing an air space near each side of the pole bridged by magnetic paths. Fig. 3 is a similar view with central and side air spaces bridged by magnetic paths. Fig. 4 is dependent part to the side of the main pole to which are attached the magnetic paths Figs. 9, IQ and 11 ei'ossin'g the air s' is a diagram of t without load when the majgnetle-paths are not inserted. Fig. Sis a 'a am sho the normal flux of the pole resu I I ting from the magnetic paths bridging the air spaces. are diagrams showin various degrees of saturation in the pa s E; and E of the pole in Fig. 8, and Fig. 12 is a diagram showmgthe field curves with and without load, with the magnetic paths inserted. I 5 I Referring to Figs. 1 to 3 the magnet core is divided into one or several parts 7) by one or several groups of air spaces a or nonmagnetic portions inserted in the same in such manner that the intermediate walls 0 separating the air spaces a om each other: form a magnetic bridge of small cross section between. the parts 12, and these alt r nate with each other in a series with the groups of air spaces in the direction-of the armature circumference. A-decrease'in the cross section of the magnet pole arises from this which results in a concentration of the flux of .the principal lines of force in the part b. One or more 'ortion's of this part b may now be so highl y saturated that the cross-magnetizing'windings of the armature are able to change the magnetic flux of this part but a very little. One way to obtain this is to make the air gap d between this part and the armature as small as possible, so that for the crossing over ofthe air resistanee only a small part of the entire magnetizing force is necessary in order that the remaining part can thus be used merely for saturating. This can be further obtained by making the air spaces a which extendnearly to the pole face 8' lyin opposite to the armature or even possib ly extending through this so great that the paths 0 remaining between them have very small cross sections and in conse uence of this are already saturated by a sma 1 total fiuX of the lines of force of the pole. The saturated part b of the pole as well as the air spaces a ne'Xt to the paths 0, offer, therefore, a very great magnetic resistance to the cross magion fietizing' flux of thelines of fo'r'ee.; By a suit- V in Fig. 4. In any case it is of advantage in tionof the ziirspaces a, well as by proper The proportions may be so selected that in running without load the saturated parts b are completely saturatedfar beyon the knee of the magnetizing curve'upon their entire len th drawn in the direction of the princi al ines of force in the pole core, so that t 1e saturation of these parts under the influence of the cross-magnetizing of the armature even under load remains always still beyond the knee of the magnetizing curve, no matter whether the cross windings of thearmature have a magnetizing or demagnetizing effect upon these parts.

he pole core is best constructed laminated. For increasing the saturation of the part b which is to be saturated, some of its plates may be substituted by nonmagnetic material, or corresponding air spaces may be inserted.

If one wishes to strongly saturate the pole horns in solid pole cores for avoiding the formation of sparks, thenthese parts which are provided with corresponding ribs and which may best be laminated for this purp ose, may be screwed upon the solid core.

he separating joints for this case are seen grooved armatures to subdivide the strongly saturated part for avoiding the all too great eddy current losses, while in smooth armatures it can be solid.

In dynamos and motors which are to be run in both directions, both pole horns of course must be in accordance with the above described highly saturated parts, so that no matter in W 'ch direction the armature re volves, the leading side of the pole will be always provided with the means embodied in my invention, to'reduce the effect of the cross-flux. Though I am mentioning in the claims only a non-magnetic space or an air space, I consider thereby also covered the modifications, showing several air spaces, as being a mere duplication of my construction.

For explaining the magnetic courses in a direct current generator, the case represented in Fig. 5 may be chosen, in which the pole core is divided into two parts I) by a group of air spaces of which one, part that lies at the leadmg' horns and has the air gap-d is highly saturated, while the other art with the air gap (1 corresponds with tiie ordinary pole construction. For the sake of sim le investigation and representation it may e further assumed that the paths 0 are exceedingly thin and the air s aces a, very broad, so that the influence oft e small number of lines of force passing through the paths is negligible and may be left out of consideration.

11 designates the linear load of the armature, expressed in amperes per centimeter of the armature circumference,

g, h designate the corresponding lengths of the pole are of the two arts bb of the pole core in centimeters. T en it is evident from the figure that the leading horn is is influenced by the cross-magnetizing windings 2 +'z .g, the trailing horn t is influenced by J; v1.7a, while at the same time at the beginning of the arc h, the cross magnetizing windings :1- z'Ja, operate altogether so that the cross windings work demagnetizing at the leading horn is and at the beginning of the arch h, and work magnetizing at the trailing horn t. It may be assumed hereby that the magnetizing ef feet of Lg upon the trailing hornt may be neglected on account of the great saturation of the part of the pole core lying over the arc g. Also the magnetic resistances in the armature core and upon the cross path through the magnet core may be neglected.

In Fig. 6 the magnetizing curves are plotted forthe parts of the passage of the lines of force which correspond at the same time to the cross magnetizing flux of force of which the abscissae of the curves represent the am tion of the single parts of the joint path of the lines of force. Curve Z stands for the part b of the pole at the leading side. Curve m for the air ga (1 under the are 9 of .2 cm. length; curve a or the teeth of 2.8 cm. length under the are 9; curve 0 for the armature teeth under the arc h; curve 1) for the air gap d of 1.1 cm. length under are h. From these values we obtain the abscissae of the magnetizing curve for the leading horn k as the sum of the abscissae of the curves Z+m-+'n, the abscissae of the magnetizing curve for the trailing horn as the sum of the abscissae of the curves 0 +1). If we take for example for the machine running Without load the number of ampere turns of the field at 0A,: 7000, then the ordinates of the points B,C represent the induction in the machine running without load in the' corresponding scale. By the loading of the armature the field Will therewould sink even to 3820'or about 51% in the ordinary form of pole with equal air gap d, between the pole 1ron and armature iron at V 5730 or onl l +m n rises quickly and all points. -Under the are 9 on the other hand the air induction falls only from 6.500 to about 12%. The greatest weakening 0 the field for the ordinary pole construction is obtained when one takes the distance to right and left from A since for this case of the entire cross magnetizing windin s h) it, onehalf works at the beginning whi e t eother works at the end of the pole arc. The ordinates of the point C,,=3820, and of the point C ==l0100 represent then the induction in the leading horn k and in the trailing horn t respectively of the ordinary pole form. If now one would permit for the new construction of .the ole an equal erc entage weakening of the eld as in the or inary c011- struction, then the point B, could change to C whereupon the proportion must arise From this there would be'necessary either A, A 8 or in our example 17 40 ampere turns, that is 25% less or one could correspondingly increase the load of the armature.

.Thus by the new pole construction a considerable saving of copper or a raising of the load which may be carried in the machine is obtained. One obtains the smallest weakening of the field if the magnetizing curve bends qulckly in maybegeasily obtained by are 9 by slight air induction under theisame, as well as by a smallest possible air gap d, which is best made as small as mechanical considerations will permit, further by suitable selection of the cross section of the part b and of the dimensions and position of the air spaces a, as well as by using iron of the highest magnetic conducthe knee which choosing a small tivity.

Fig.7 shows the field curves of the machine runnin with full load and without load, in whic the air induction under the pole arcs is represented-as the ordinates depending upon the armature circumference wherein like numbers correspond to the same points of the pole arc in Figs. 6 and 7. One may see that the commutating field and thus the commutating E. M. F. under the brush corners changes'only insignificantly.

Thus far, the discussion relates only to the case in which the ma netic paths are extremely thin and thus the effect oi the same is to be neglected. f

In the following may now be explained the principal difference which characterizes the arrangement of the magnetic paths in ordinary form. It consists mthat a special division of lines of force is caused b the same, in such manner that a considerab. e diminishing or prevention of the total cross-magnetcream? izing is obtained,'=which"'latter makes possible a still further'flconsidereble saving of copper.

- For the followin "explanation the'already treated consideration of Fig. 5 ma be selected, which in order not to over oad the drawings is re resented a ainin Fig. 8.

- For the sa 0 of sim "city "let; here,the already characterized highly saturated part at the left of the recess.a be'indicatedby D, l the part to the right of the'recess a as a whole be designated by (E left and E r1 ht). A roup of air spaces may he called in the following merely recesses. Besides the discussion deals only with a constant magnetic excitation.

If one considers first that the paths are omitted, then in runnin without load the same induction will infiu'ence the-part throu hout. brought about that a certain'numberof lines of force pass over to D .bythepathsfrom E in consequence of the difference in magnetic entire length of D, because of the-high saturation of the portion Dproduced by the small air gap which the lines of force passing through D have to cross in order to get to the armature, compared with the large gap separating pole portion E from the armature. Owing to the considerable length 0 the pole arc of this part D, a small air in uction'is produced at the same'time; -Hence only *a' comparatively small number of ampere turns is used for drivin the lines of force through this air gap, whi e by far the largest part of ampere turns is used for saturating the part D. v The. flux of lines of force'through the air spaces may bedisregarded sinceit is slight. Consequently in the art E a greater number of lines of force will ilow than formerly since now besides those lines of force which were resent also in the'first case and which pass rom the magnet iron through the air s ace into the armature, still others arise w ich pass over from E to D. By this, however, a greater saturation arises in E, and will be the highest in the vicinity of the recess a. The lines of force are somewhat crowded together and made more dense toward the recess a. All increase of the saturation, however, involves a decrease inthe cross-magnetizingas is well known, and thus also a diminution in the drop in voltage of the machine. Considered exactly the relations which now arise are as follows: If one designates with N the entire number of lines of force which pass out of one pole into the armature, further the number of lines of force of-the part D with N those of E with N then in the case without an arrangement of paths we get N N, N,. If now one has the same outer dimensions of the pole as well as the air ga of the pole arc also'in the case with paths, t en after Ewhile its parts with E; E,

potential prevailing atdiflerent points of the i out paths, and what the insertion of the same 'N increases because of the now lower ma etic resistance, while at the same time N owers because of the now arising somewhat higher magnetic resistance. The sum N of the two will, however, remain about the same or be even greater than before. The principal point of difference and at the same time advantage is, however, the fact that in E an unequal saturation occurs, whose highest value is considerably greater than in the case withis most important of all, as will be shown hereafter, that the greater saturation occurs at the part of the pole upon which the armature wires aflect the greatest weakening; that is, in the selected example in the vicinity of the recess a. Besides it is evident from this that this higher saturation will be obtained without any extra expensefor magnet copper, but takes lace automatically at the same time with t e inserting of the paths.

. The lines of force crossing over from E to D will enter horizontallyor almost horizontally into the paths in Fig. 8, while they are directed downwardly at a slight distance from the recess a. The course of the lines offorce can be represented somewhat as arcs of a circle (Fig. 8), so that the. territory of the hi her saturation. can be bounded on the right by the line qr, and below by the arc v. The lines of forcewill really spread out somewhat at this point, but one can obtain a sharp boundary at the right for instance by inserting a recess a, in which the paths would naturally be omitted for this purpose. One can obtain the same effect also at the place over the recess a in the same manner as shown forexample bythe dotted lines. For the purpose of a graphic re resentation the -osition of the recess '11 may e so chosen that its middle line which is in this case the line 1' coincides with the middle of-the pole arc In this place the effect of the armature wires lying under E equals Ofiwhile the magnetic pressure of the same increases to left and right so that the total magnetic pressure upon the side E gets less and is increased u on the side E While thus in the case in w ich no paths are used, the magnetizing curve because of the slight and at all laces equal saturation of the iron has an a most strai ht line course and holds for the entire arc curves 0 p of Fig. 6 of the drawings are used will hold only for the right half, while it is very much more curved for the left half E and strives to follow more the course of the curves 1+ m +n. The condition that the air induction under -E because of the now somewhat higher saturation of the part. E becomes a little bit smaller, works favorably for this. A glance at Fig. 6, as well as Figs. 9, 10 and 11 of the drawings, which latter will hereafter be explained, shows, however,

this form somewhat as that of the.

enses field of E=must becbme less. Bywpe'rsee lection of the'relations the str E cannot only madto entire y compenssate for the weakening of E but even surpass it and therewith increase the total number of lines of force as well from E as also those of the entire pole which gives a considerable saving of copper in the ma et winding. By this one thushas in hand a new means 'to compound in a simple and exceedin ly cheap manner shunt wound machines. aturally the smallerthe loss of tension is in the armature, the easier will it be to obtain this.

In Figs. 9, 10 and 11, these various re ations are graphically represented and set forth, wherein the curves F represent the magnetizing curves for the part E for the various de rees of saturation, the curves G represent t ose for the part E for a considerab y lower but in all three cases about equal degree of saturation. The point I corres onds to the middle of the pole arc of E. 'le thus the distribution of the lines of force under the pole are E in running without load takes place along the horizontal line H-H, measured upon the scale for each half (that is, it would constantfor each half of the are) it would result in running under load along t-he'stron ly drawn out-portions of the curves I-P, -K, whose ordinates now represent the air induction along the are E. In this Q$ indicates the number of ampere turnsoi the field, RS and S-T represent the cross magnetizing windings of the armature under E for E and E,. The three figures show that with increasing saturation of E the weakening of that part which is represented by the simple hatched portions become smaller and smaller, so that finally the strengthening of E which is represented by the double hatched iortions preponderates as F1g. 11 shows. 11 this case thus the above mentioned increase in the number of lines of force in the iple would take place. Considering now furt er (which is not shown in the drawings) that the air induction under E is somewhat less than under E,, and that thus the scale for the former must he corres ondingly reater, then the o eration just escribed w' only be further aided, which follows without further'discussion.

A few figures will explain somewhat more exactly the relations. It may be for example that the roportion of the cross section of the iron pat s to the intermediate air s aces is taken-as 1: 4 and for the sake of s'nnp icity the thickness of the paths may be 2 'm-m,

and the width of the air spaces 8 mm. Then the workingout of an example when,

' be obtained in all is thus at once evident. In a suitable selection of the construction these numbers may be easily modified so that they correipond to the proportions represented in the 'gs. 9, 10 and 11. It may be further observed that the loss of potential occurring in E is of little influence upon the number of lines of force passing'throughthe paths on account of the almost straight line course of the magnetizing curve at very high saturation.

In order to keep the induction D constant upon theentire length and to thereby obtain the most favorable form of the megnetizin curye for this part, one need 0 y place t e recess a somewhat obliquely, that '18, so that the cross section of the material of the part D-decreases toward the top as the figure shows.

The corresponding field curves in runnin without load and an under load with reference to the influence of the'paths are shown in Fig. 12 wherein here also as in the former Figs. 6 and 7 equal pro ortions of the Figs. 9 to 12 correspond to li e points of the pole arc.

From theabove it is accordingly evident that the more highly saturated parts there are present the smaller will be the totalcross ma etizing or distortion of the magnet fiel It is not necessary that all arts of the ole be saturated with equal strength. ince the effect of the cross windings decrease toward the middle of the pole, the parts lying near the middle may also receive a smaller degree of saturation than for exam Is the po e horns. This case is represented in Figs. 2 and 3, which also show at the same time the construction with several roups of air spaces. Here the most hig y saturated parts are shown at the pole horns, while the parts lying toward the inner portion of the magnet core can receive the desired degree of saturation by means of the paths.

By a suitable selection of the proportions the same or almost the same saturation may parts of the pole in running under load. Likewise under certain conditions the induction in the air under the entire arc of the pole can be brought to'the same or substantially the same value.

The above considered construction in Figs. 5 and 8 is the most suitable with, relation to the prevention of the weakening of the flux of lines of force, however, the number of constructions may be considerably increased;

because the effect of the paths is always present as soon as there is a difference in mag netic potential. in the present invention, or atleast can be made so in all cases by proper dimensiom'n Further it is neither necessary that the axis of an entire; group of air spaces extend in the The latter is ever the same 1 direction of the armature axis, nor that the principal lane of an air space stands. erpendiculary to the armature axis. ,T ese orms are only'shown in the drawings for the sake of sim licity and economy in construction, still t e desired purpose or the effect suitable to the particular purpose of themachine may always be obtainedalso fore onstructions differing. from-those by a proper dimensioning. For example, instead of placing the recess obliquely as above mentioned in order to produce a magnetic difference of potential upon the. entire length of D of 8, one ma also place the recess parallel to the-boun ary surface of the core and obtain the desired division of the material for obtaining a difference in the potential by cutting out some of the lates corresponding thereto in the part D. inally the paths in.

"general have at the same time the further mechanical advantage that they contribute.

to the solidity of the entire magnet bod Especiall in such cases in which for examp e the part ying at the pole horns is very long and narrow and besides the recesses are open below, there is the danger that'a vibrationof this part occurs by the magnetic pull which under certain conditions may result in grindin of the magnet iron against the armature. iesides, this disadvantage can also be increased by the weight of the magnet coils which in assembling are forced generally against the frame with a certain ressure in order to prevent a movement 0 the coils. In poles which are laminated the assembling of the magnet pole itself is made thus con siderably easier. The advanta es of the new l1pole construction are accor ingly principa y as follows: (1) The s ark formation is prevented by reason of the igh saturation of the pole horns. (2) A higher load figure of the machine or a corresponding saving in the magnet copper is obtained by the high saturation of the pole horns. ent pole construction has over other known constructions the rincipal advantage, that on account of the Favorable division of lines of force brought b the magnetic intermediate walls the tota cross magnetizing (that is at the same time the distortion of the magnet field as also principally the weakening of the same by the distortion) is at the same time not only reduced to the smallest possible amount but the weakening of the field is even entirely done away with and in a favorable case even in running under load gives rise to an increase of the entire flux at the (3) The prestamed.

the alternating current machines and rotaryconve-rters may have the new pole construction applied to them. In these rnach-ines in phase s ifted currents a react-ance is effected in the regular magnet fieldwhich principally relates to the polehorns and operates in a 'magnetizin'g or demagnetizing manner upon the same. in single phase converters the armature reactance, even when the current has no phase shifting, is of an oscillating nature and in the maximum equal to the full valueof the direct current armature reactance besides constantly alternating its direction. An oscillation of the intensity of the field upon the armature circumference is caused by this, which can make a .sparkless working of the direct current side impossible. Having thus described my invention, the following is what I claim as new therein, and desire to secure by Letters Patent:

1. A pole piece formed with a non-magnetic space or part producinga tapering away\ from the ole face of part of the leading orn side 0 the ole, and having magnetic bridges adapte to lead part of the main flux of the'pole across and into said tapering portion of the leading horn side thereof.

' 2. A pole'piece formed with, a non-magnetic space or part producing a tapering,

away from the ole face, of part of the leading horn side of the pole, and having magnetic bridges in the non-magnetic space or part connecting the main interior portion of the pole with said tapering portion of the leading horn side thereof.

3. A pole piece formed with a non-magnetic s ace or part dis osed eccentrically to the po e axis and dividing the pole into a plurality of portions and magnetic material extending from one of said portions through said non-magnetic space or part and leading to the other of said ortions of the pole.

4-. A pole piece ormed with a non-magnetic s ace or part disposed eccentrically to the po e axis and approaching the pole axis toward the ole face and dividing said pole into a plura ity of portions, and bridges of magnetic material extending from one of portions throu h said non-magnetic space or part and lea ing to the other ofsaid portions of the pole.

5. A pole piece formed with an air space disposer eccentrically to the pole axis and dividing said pole into a plurality of portions, and transverse bridges of iron extending through said air space and connecting the portions of the pole together.

6. A o'le piece formed with an air space dispose eccentrically to the pole axis and approaching the pole axis toward the pole face and dividing said pole into a plurality of portions and transverse-bridges of-ironextending through said air space and connecting the portions of the pole together.

7. A pole piece having an independent member of magnetic material secured to the leading horn side of the pole with a non-magnetic space or. part between itself and the pole and magnetic paths extending across said non-magneticspace or part and connecting said independent member with the main portion of the pole.

8. A pole piece having an independent member secured to the leading horn side of the pole with an air space between itself and the pole and iron paths bridging said air space.

9. A pole-piece having an independent member of magnetic material secured to the leading horn side of the pole with'a non-mag- 1 netic space or pole at a suitab e distance fromthe pole axis and approaching the pole axis toward the pole-face, and magnetic paths extending across the said non-magnetic space or part and connecting said independent member with the main portion of the pole.

' 10. A pole-piece having an independent art between itself and the member secured to the leading horn side of the pole with an air space between itself and the pole at a suitable distance from the pole axis and approaching the pole axis toward the pole-face, and iron paths bridging said air space. I

11. A pole piece formed with a non-magnetic space or part producing a tapering,

away from the ole face, of part of the leading orn side 0 the pole throughout the entire length of said space or part, and having magnetic bridges in said non-magnetic space or part connecting the main interior portion of the pole with said tapering portion of the leading horn side thereof.

, v HEINRICH BOTH.

Witnesses-z I H. ALFRED JA KE, HENRY ENnERs. 

